Practice question

Somatic hybridization involves fusion of protoplasts isolated from somatic vegetative tissues of different species cultivars or genera, bypassing sexual incompatibility barriers that prevent conventional crossing due to pre zygotic pollen stigma incongruence or post zygotic endosperm abortion. Protoplasts are obtained by enzymatic digestion of cell walls using cellulase Onozuka R-10 and macerozyme releasing naked cells bounded solely by plasma membrane maintaining totipotency to regenerate wall and divide. Mixed protoplast populations labeled with different fluorescent markers or selectable complementation traits are induced to fuse using polyethylene glycol PEG with calcium at high pH causing membrane dehydration and coalescence or by electrofusion using alternating current for alignment and direct current pulses for reversible membrane breakdown forming heterokaryons containing mixed cytoplasms and nuclei. Fusion product nuclear fusion may produce symmetric somatic hybrid allotetraploid containing both parental chromosome sets or after chromosome elimination asymmetric hybrids carrying partial genomes. This technique enabled transfer of polygenic traits disease resistance abiotic tolerance cytoplasmic male sterility from wild relatives to crops, exemplified by pomato potato plus tomato fusion and citrus somatic hybrids for rootstock improvement.